The instant invention relates to a process for conglutinating (i.e., gluing together) wood particles into formed bodies, and to the binder-free formed bodies produced by the process, in particular, board-shaped material.
Particle boards and wood fiber boards are valuable materials which can be made of a self-regenerating raw material, i.e., materials such as lignocellulose-containing wood. These wood materials are used in many different areas of manufacture as the basic material. Mainly the furniture industry, the automotive industry, the packing industry, the construction industry, etc., are involved here. Heretofore, particle boards and wood fiber boards were generally mixed with binders, were formed, and then pressed under heat and pressure. So-called medium-density fiber (MDF) wood fiber boards are normally made of wood chips from needle or leaf bearing trees produced in chippers, e.g., the chips are reduced by means of so-called refiners to the desired fiber size and fiber thickness. The wood fibers are normally glued or conglutinated with synthetic resins and are dried to a desired degree wood fiber humidity. The binder-coated wood fibers are then deposited by machine in a forming station on a conveyor belt (MDF boards), or are deposited on a sieving belt.
Depending on the desired range of apparent density, insulating boards (230 to 400 kg/m.sup.3 apparent density), medium-hard wood fiber boards (350 to 800 kg/m.sup.3 apparent density), as well as MDF boards (approximately 650 to 900 kg/m.sup.3 apparent density), and also hard fiber boards (approximately 800 to 1,200 kg/m.sup.3), are produced.
Compression into the board-shaped materials can be carried out in a discontinuous operation as well as in continuous operation presses, the so-called pass-through or conti-machines.
In addition to these board-shaped materials, processes using fibers prepared in this manner are also known in which a two-phase or multi-phase pressing process makes it possible to produce so-called "fiber form elements." The fiber form elements are normally pre-pressed into a blank in a first pressing process, wherein the essential hardening reaction is not completed, i.e., is at first only a partial one.
The "mats" which are thus obtained, and which may furthermore contain additional web/fabric inserts, are already sufficiently firm after the first pressing process to be handled and are brought to their final form in a second pressing process. This can be achieved by means of an appropriate pressing tool which reflects the form of the finished product and imparts it to the product.
MDF as well as wood fiber and particle boards are normally conglutinated with binders, e.g., uric formaldehyde resins, melamine formaldehyde resins, phenol formaldehyde resins, and/or diisocyanates as the binding components. The quantity of the binder generally amounts to approximately 3 to 15% of the weight of the wood fiber or wood chip quantity (abs. dry). The quantity of binder depends in this case among other factors on the type of binder and on the type of wood fiber or wood chip, as well as on the mechanical and technical properties of the raw wood materials.
In addition to binders based on synthetic materials, biologically-based binders have also proven themselves. According to DE 30 37 992 C2, the lignin sulfonate obtained in cellulose production is mixed with enzymes obtained through biotechnological means and is mixed into the wood fibers or wood chips as a binder. The enzymatic catalysis then causes the "hardening" of the lignin phase, so that the wood fibers or chips conglutinated into the binder solidify. This system consisting of binder and enzyme can practically be viewed as a "biological two-component adhesive" in which the lignin sulfonate could be the adhesive component and the enzyme the hardener. This process requires the utilization of lignin sulfonate as the binder in the process for the production of the formed body, in particular of board-shaped material.
An operating procedure in the production of low-emission binders for work materials containing wood or cellulose is described in DE 36 44 397. It is a disadvantage of this process that it is still necessary to use a binder based on synthetic resin which, together with the lignin and lignin-like waste materials, such as sulfite waste liquor, must be mixed with the lignocellulose-containing material before pressing.
The object of the present invention is to provide a process which can be used without the addition of a binder, but merely through the action of an enzyme upon a lignin which has not been chemically pre-treated to produce formed bodies, in particular board-shaped basic material of comminuted wood particles which can be processed at least in part in conventional plants or plant sections such as described earlier in the state of the art. It is also the object of the instant invention to create formed bodies, in particular board-shaped materials, from lignocellulose-containing materials and containing no additional binders.